Devout Muslims believe that the black stone represents all of Allah's power and glory. They believe, sincerely, that if the USA launched rockets at Mecca, Allah would swat them away like flies, or turn them around to hit New York or Washington.
If Allah could not stop the”infidel” bombs, and Mecca was turned into a crater, this would constitute absolute proof that Muhammed was a fraud and a liar, and that the moon-god rock had no power after all.
This would mean the end of the entire cult of Islam. Their cult could not adapt to or respond to or overcome complete, visible proof that Allah was powerless to stop the infidel weapons.
Now, I'm not calling for or predicting Mecca will ever be bombed. Not unless American cities were destroyed by Islamofascist nuclear bombs first. Our insane enemies don't care if we threaten Cairo or Damascus. They would welcome such attacks, as providing mega-martyrs for Allah! Polls conducted in many Islamic nations have asked, "Would it be worth it to wipe Israel off the map with atomic bombs, if it meant millions of Muslims would die in the counterstrike?" The poll is answered YES! by high numbers. So targeting cities means nothing to our fanatical enemies.
Mecca, on the other hand, means everything to our enemies. Some of our semi-rational enemies must understand that if they nuke our cities, they may finally get a test of Allah's power to smite incoming missiles before they can hit and destroy Mecca and Allah’s black moon-god Ka’aba rock. These semi-rational enemies must understand this, so that they can influence the complete maniacs, and keep them from ever getting the nuclear weapons they would surely use against America, given the chance.
The semi-rational Islamists must understand that Mecca and Allah's all-powerful black moon-god rock are on the table, as a retaliatory target, if our cities are attacked with nukes.
Putting Mecca on the counterstrike target option list, even hypothetically, means far, far more to them than threats to change Arab regimes or bomb Muslim capitols.
I want the insane and semi-sane Islamofascists to understand this: nuke America, and Mecca is on the retaliation list. This is the only meaningful deterrent threat, to insane and semi-sane Islamofascists. If you wish the sane Muslims and semi-sane Islamists to influence the Islamofascists away from WMD attacks on the USA, let it be known that the very existence of Mecca, (and therefore their entire religion), is on the table.
(And don't bother with the trite comparison of Mecca and say, the Vatican. The Vatican is just the place the Pope hangs his miter. Catholics don't literally lay down and worship some idol in St. Peters 5 X a day, for 20 minutes. If Rome was nuked, it would not destroy Christianity. Christianity lies in the heart of each believer, in the concept of Jesus the Savior on the Cross, not in worshipping some physical idol or totem like Allah's black rock.)